1. Field of the Invention and Related Art Statements
The present invention relates to a method of electrically blasting one or more detonators electromagnetically coupled with a bus wire via one or more magnetic cores by supplying a high frequency electric current to the bus wire. The invention also relates to an electric cordless detonator for use in said electrical blasting method.
In a Japanese Patent Application Laid-open Publication No. 86400/85 (corresponding to U.S. Pat. No. 4,601,243 issued on July 22, 1986), there is disclosed the method of electrically blasting a plurality of detonators which are electromagnetically coupled with a bus wire with the aid of transformer magnetic cores by supplying a pulsatory high frequency current to the bus wire. FIG. 1 is a schematic view illustrating this known method. To an electric blasting device 1 comprising an electric power source and an oscillator for generating the high frequency current, is connected a bus wire 2 having a loop portion 2A with which a transformer magnetic core 3 is electromagnetically coupled. With the magnetic core 3 is further electromagnetically coupled a loop-like wire 5 electrically connected to a fuse head of a detonator 4. When the pulsatory high frequency current is supplied from the electric blasting device 1 to the bus wire 2, a high frequency current is induced in the loop-like wire 5 via the magnetic core 3 by means of the electromagnetic induction. Then, the fuse head in the detonator 4 is heated to fire and a detonating explosive is exploded.
In such a method, a pair of leg wires of the detonator are connected in the form of the loop wire 5, and thus leg wires are considered to be always short-circuited from the operation of coupling the loop wire 5 with the bus wire 2 via the magnetic core 3 to the actual explosing operation and the electric energy is hardly introduced into the loop wire. Therefore, any undesired explosion of the detonator can be effectively prevented.
In the above explained known method, the detonator is the same as an ordinary detonator except for a point that the leg wires are short-circuited into the loop. Therefore, if the loop wire were to be cut or an insulating sheath of the wire were to be broken, the electric energy could be introduced into the wire and the detonator might be accidentally exploded.
In such an occasion, the known blasting method could remove undesired explosion only to such an extent that ordinary blasting methods can attain.